maths

The answer is 65/24.

2013-07-07 07:02:03 補充：
In triangle ADE
AE^2=AD^2+DE^2
AE = square root(144+25) = 13
AG = 6.5

In similar triangle ADE & AGF
AD:DE = AG:GF
12:5 = 6.5:GF
GF = 6.5x5/12 = 65/24

2013-07-10 11:56:46 補充：
In triangle ADE
AE^2=AD^2+DE^2 <====根據畢士定理
AE = square root(144+25) = 13 <=====AD是12，因為這是一個square
AG = 6.5

In similar triangle ADE & AGF
AD:DE = AG:GF <====兩相似三角形，邊與邊比例相同
12:5 = 6.5:GF
GF = 6.5x5/12 = 65/24

可以詳細解釋一吓嗎
(Please show step)